Process of phosphating in a trichlorethylene vapor zone



July 11, 1961 F. G. Low 2,992,146

PROCESS OF' PHOSPHATING IN A TRICHLORETHYLENE VAPOR ZONE Filed Feb. 26,1959 FREDERmK C1. Lew

ATTORNE Y United States Patent a corporation of Delaware Filed Feb. 26,1959, Ser. No. 795,870 2 Claims. (Cl. 14S-6.15)

This invention relates to a process fori metal treatment and, moreparticularly, it relates to a process wherein metal articles arecontacted with aqueous treating solutions within a chlorinatedhydrocarbon vapor zone.

Aqueous solutions are frequently employed to treat metal surfaces inorder to impart corrosion resistance and improve paint adherence. Ingeneral after cleaning (usually by alkaline washing), metal articles maybe initially treated with an aqueous activating solution containingtitanium salts and oxalic acid. Thereafter, the activated surfaces arecontacted with an aqueous phosphatizing solution and then treated Withan aqueous passivating solution containing a chromate sealer. Each ofthe above steps is conveniently followed by subjecting the articles to awater rinse.

In addition to the above sequence of aqueous treating steps, commercialpractice also embraces metal degreasing, painting, etc., with nonaqueoussolutions under a chlorinated hydrocarbon vapor zone. -The use of avapor zone has the advantage of excluding air and other corrosiveinfluences during treatment.

The present process relates to the treatment of metal surfaces withaqueous solutions under a chlorinated vapor zone whereby the advantagesof both aqueous treatment `and a vapor zone are realized.

It is an object of the present invention to provide an eifective processfor treating a metal article with an aqueous solution under achlorinated vapor zone.

It is a further object to provide a process for treating a metal articleby spraying the article with an aqueous solutionv within a chlorinatedhydrocarbon vapor zone.

'I'hese and other objects will be apparent in the following description.

It has been found that aqueous treating solutions may be sprayed withina chlorinated hydrocarbon vapor zone under certain conditions withoutunduly disturbing the vapor zone and that articles'within the vapor zonemay be treated in an air-free atmosphere.

When using a trichlorethylene vapor zone, the aqueous treating solutioncan be sprayed into the vapor zone at a temperature range `fromapproximately 65 C. to 90 C. without causing serious disturbance of thevapor zone. An optimum range for spraying of the phosphatizing solutionwould be 78 to 85 C. in order to cause little or virtually nodisturbance of the established vapor zone. Spraying the treatingsolution into the trichloroethylene vapor zone at a temperature belowapproximately 65 C. will cause disturbance of the vapor which isevidenced by a physical lowering of the vapor zone-air interface becauseof a lack of sufcient heat input; as a result vapor degreasing of acontaminated part will give poor cleaning results and the coated articlewill dry very slowly when placed in the vapor zone. Spraying thesolution into the trichloroethylene vapor at a temperature aboveapproximately 90 C. will cause inadequate control of the vapor zone andtrichlorethylene may boil out of the apparatus, resulting inconsiderable waste.

Perchlorethylene may be substituted for trichlorethylene in the processprovided that temperature conditions are altered in order to maintain avapor zone and prevent undue contamination and wastage. lSinceperchlorethylene boils at a higher temperature than trichlorethylene,

the temperature of the phosphatizing solution should be considerablyhigher.

As in the instance of trichlorethylene, the aqueous solution ispreferably sprayed at a temperature between the azeotropic boiling pointof the water-solvent mixture and the boiling point of the solventitself. Maintaining the temperature of the spraying solution below theazeotropic boiling point vincreases the degree of condensation of thesolvent and collapses the vapor zone; a temperature in excess of thesolvents boiling point results in excessive evaporation of the water andcontamination of the boiling solvent 17 which in turn prevents thetreated article from properly drying.

The treating solution used may be any conventional aqueous spraysolution, and those solutions indicated in the examples are merelyrepresentative. Typical phosphatizing solutions include acid salts ofzinc phosphate and iron phosphate together with phosphoric acid.

A suitable passivating solution contains small amounts of chromic acidbut, in addition to chromic acid washes, other conventional passivatingsolutions can be similarly employed. Many of Ithe commercial passivatingsolutions are proprietary solutions of monoor dichromate salts thatinclude mineral and organic acids. These and aqueous solutions designedto activate metal surfaces prior to phosphatizing are also adaptable4for use in the present process. Aqueous solutions containing smallamounts of such activating agents as titanum salts and oxalic acid canbe readily applied under the conditions prescribed herein.

In one embodiment of the present invention, a metal article can becontinuously treated under a chlorinated hydrocarbon vapor zone. Thearticle can be cleaned initially by vapor degreasing, thereafter treatedwith an aqueous phosphatizing solution and then retained in the vaporzone to insure water removal. It is to be understood that aqueousactivating and chromate solutions can be applied before and after thephosphatizing solution is used. All oi these steps, including any waterrinses before and after the treating solutions have been applied, arecarried out under a single vapor zone.

In another embodiment, a metal article can be vapor degreased, immersedor sprayed with a nonaqueous phosphatizing solution and then moved tothe spraying compartment for treatment with a hot aqueous chromatesealer. In this embodiment, the `first compartment, instead ofcontaining degreasing solvent, contains a nonaqueous phosphatizingsolution, such as trichloroethylene, 0.1-1% b-y weight of phosphoricacid and a small amount (2-l2% by weight) of butanol as a solubilizer.The metal article is immersed in the phosphatizing solution for 30 to 60seconds and then moved into the spraying compartment.

Referring to the drawing, the single figure is a crosssectional view ofa tank used in carrying out the process.

A vapor degreaser tank, 10, is provided with insulated walls surmountedby cooling coils in which the cooling fluid enters at 12 and leaves at13. Condensate from these coils is collected in a circular rimmed gutter15 which runs around the top section of the degreaser tank under thecooling coils. The cooling coils establish a vapor zone and constitute abarrier, preventing solvent vapor from rising above the coils. Anycondensate within gutter 15 is drawn off through pipe 16 to a phaseseparator in which the solvent is recovered from admix-ture with water.

The degreaser is separated into two compartments by partition 11. Onecompartment contains degreasing solvent 17 which is kept at the boilingpoint by a heating coil fed with steam or a heated fluid entering at 18and leaving at 19. Contaminated solvent may be removed as desiredthrough pipe 20 which is equipped with a valve for this purpose. Theother compartment is reserved for Patented July 11, 1961 applyingaqueous treating solutions which enter the degreaser tank through pipe2-1 and spray-head 22. The excess solution collects at the bottom of thecompartment 24 and is drained olf through pipe 23, equipped with avalve. The solution is preferably sprayed on article 27 although othermethods of applying the solution, such as dipping, will suggestthemselves.

The process is carried out by adding solvent 17 to the solventcompartment and heating so that the entire degreasing zone is filledwith solvent vapor and the vapor level extends up to the cooling zoneforming a vapor-air interface 30 in the approximate location indicatedby the dotted line. When trichlorethylene is used as the solvent, theaqueous solution is heated to a temperature between 65 to 90 C.,preferably 78 to 85 C., and passed continuously into pipe 21 through thespray-head 22 and removed continuously through pipe F23. An article, 25,to be degreased is then lowered by support 26 into position over theboiling solvent. Of course, extremely dirty articles may be dipped intothe liquid solvent 17. When thoroughly degreased, the article is thenmoved into the spray as indicated by the position of article 27 held bysupport 28 Where it is treated by spray contact with the aqueoussolution. Following this, the article may then be moved back to thedegreasing position of article 25 until thoroughly free of moisture andthereafter lifted out of the degreaser.

Moisture is completely removed from the phosphatized article byazeotropic distillation with solvent vapor, which becomes condensed onthe cooling coils at the top of the degreaser, drained through outlet 16and recovered from the solvent condensate by means of a conventionalphase separator (not shown). Any water which appears in the boilingsolvent 117 is rapidly vaporized by azeotropic distillation whereupon itcondenses on the coils so that the solvent 17 remains substantially freeof moisture.

Under operating conditions, the treating solution remains substantiallyfree of solvent. If some of the solvent condensate mixes with aqueoussolution 24, and is not completely removed by azeotropic distillation,it can be readily removed by use of a phase separator. The aqueoussolution is recirculated as desired and if the boiling solvent becomescontaminated, it can be removed and purified by distillation.

The apparatus for the invention is of such design that a singlechlorinated solvent vapor zone, preferably trichlorethylene, ismaintained throughout, although the above procedure involves severalsteps. The first part of the apparatus is a conventional vapor degreaserand is the means for generation of the solvent vapors for the apparatus.The second part of the apparatus consists primarily of a spray apparatuswith a catch tank for catching and drawing off the aqueous solutionafter spraying through the trichlorethylene vapor zone. The third stepmay be carried out in any part of the apparatus, being merely a vaporzone treatment for removing the water from the article. In the apparatusshown in the drawings, the degreasing zone may be employed for thatpurpose. If desirable, the apparatus can be designed to include othersteps. For example, a painting step can be integrated in the process andalso carried out within the vapor zone. Preferably, the paintingsolution would have as a thinner the same chlorinated hydrocarbon-usedas the solvent.

In operation, the aqueous treating solution sprays through the vaporzone into its catch tank, absorbing little or no solvent if properconditions are used. It any solvent does condense in the aqueoussolution, it distills out during the operation. Therefore, although thesolution is sprayed through a solvent vapor zone, it is essentially freeof solvent. Vapor condensate collected in the vicinity of the sprayingoperation possibly will contain some water as well as solvent. Anycondensate collected in the apparatus is drained olf through a waterseparator beforethe solvent is returned to the machine. The waterseparator will effectively remove the water from the trichlorethylene.Spraying the aqueous phosphatizing solution in a trichlorethylene vaporzone, unexpectedly, does not cause a destruction of the solvent 'vaporzone or a lowering of the solvent vapor line if the proper conditionsare maintained; nor are any ghost vapors formed in the trichlorethylenevapor zone.

Example 1 A measure of 103. 5 grams of Fosbond 10 (azinc dihydrogenphosphate solution produced by Penn Salt Manufacturing Company) is mixedwith 0.8 gram of Phosbond 10A (a nitrite compound prepared by Penn SaltManufacturing Company) and dissolved in 5 liters of water. Next, `6.4grams of solid sodium hydroxide is added and dissolved in the solution.This solution is heated to 70 C. A vapor degreaser is set up whichcontains a catch tank within the trichlorethylene vapor zone. A steelpanel is degreased in the solvent. vapor zone out.- side the phosphatespray area, suspended in the phosphatizing spray for approximately 3minutes, then suspended in the trichlorethylene vapor zone outside thespray area again for about 2 minutes to dry the panel. The panel is thenremoved from the vapor zone and is dry with a gray zinc phosphatecoating.

Example 2 Example l is repeated except the phosphatizing solution isheated to and sprayed at a temperature of C. instead of 70 C. Verylittle disturbance is observed in the vapor zone. A gray zinc phosphatecoating, similar to that obtained in Example l, is imparted to thepanel.

This method is applicable for any commercial aqueous phosphatizingsolution which can be sprayed in the 65 to 90 C. rangeA and includesiron phosphate and manganese phosphate coatings as well as zincphosphate coatings. The coatings can be applied to zinc, aluminum andcadmium surfaces as Well -as to steel, although steel is by far the mostcommon metal treated.

Example 3 Example l is repeated and the phosphatizing step is followedby a water spray rinse dispensed through head 22 to insure completeremoval of excess phosphatizing chemicals. The water temperature of thespray rinse is the same as that of the phosphatizing solution. Followingthe spray rinse the panel is dried by suspending it in thetrichloroethylene vapor zone as in Example l.

Example 4 Example 3 is repeated and a conventional ehrornic acid rinsestep follows the phosphatizing step. The chromic acid rinse contains 1/2pound of acid per 100 gallons of solution. yacid rinse is also sprayedthrough head 22 in the trichlorethylene vapor zone at the sametemperature as the phosphatizing solution. After the chromic acid rinse,the panel is dried by suspending it in the solvent vapor zone as inExample 11. The chromic acid rinse serves to pacify the phosphatizedarticle and the article may then be either dip or spray painted withoutbeing removed from the vapor zone.

Example 5 A steel panel that has been immersed in the phosphatizingsolution of Example 1 is placed in the spraying compartment and a hot(80 C.) chromic acid rinse containing 1/z-pound of acid per 100 gallonsof solution is dispensed through head 22. The panel is sprayed for 2minutes and then retained in the compartments vapor zone for severaladditional minutes until all of the water is removed. The phosphatecoating is passivated and the panel displays excellent resistance tocorrosion.

When trichlorethylene is employed as the solvent, it is important -tonote that an optimum temperature range for aqueous treating approximatesthe optimum temperature range for degreasing with the solvent. Inaddition,

the preferred temperature range is between the azeotropic boiling pointfor a water-trichlorethylene mixture and the boiling point of thesolvent itself. In addition to the above advantages, the process may becarried out with little or virtually no loss of expensive solventbecause the spraying temperature causes little disturbance to thesolvent vapor, and any solvent-water mixture that results can be easilycollected by condensation and readily separated by simplephase-separating means.

Accordingly, the essence of the present invention is the step ofspraying an aqueous treating solution Within a solvent vapor zone at atemperature that results in a minimum disturbance to that zone and isbetween the azeotropic boiling point of the water-solvent mixture andthat of the solvent itself.

Trichlorethylene is `admirably suited as the solvent because it is anexcellent degreaser, paint thinner and drying medium. Any slightcontamination of the solvent with the aqueous solution is easily removedby phase separation, and since many of the treating agents are acidswith high yainities `for water, the solvent is not adversely alected bythe action of these acids.

Perchlorethylene is not as suitable `as trichlorethylene because itsboiling point is above that of water and unless the solvent isvigorously boiled, the vapor zone will collapse. In addition, -anexcessively large mixture of that solvent and the phosphatizing solutionwould result. Methylene chloride is likewise unsuitable as compared withtrichlorethylene since the formers boiling point is so low that thearticle could not be dried -in the vapor zone and methylene chloride isrelatively soluble in water.

This application is a continuation-impart of my copending applicationSerial No. 732,291, led May 1, 1958, now abandoned.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In a process for treating a metal article, the step of contactingsaid article with an aqueous phosphatizing solution at a temperaturebetween and 90 C. Within a trichlorethylene vapor zone.

2. In a process for treating a phosphatized metal article, the step ofcontacting said -article with an aqueous passivating solution at atemperature between 65 and C. within a trichlorethylene vapor zone.

References Cited in the le of this patent UNITED STATES PATENTS2,674,552 Callahan Apr. 6, 1954 FOREIGN PATENTS 1,082,916 France June23, 1954 1,134,177 France Nov. 26, 1956

1. IN A PROCESS FOR TREATING A METAL ARTICLE, THE STEP OF CONTACTINGSAID ARTICLE WITH AN AQUEOUS PHOSPHATIZING SOLUTION AT A TEMPERATUREBETWEEN 65* AND 90*C. WITHIN A TRICHLORETHYLENE VAPOR ZONE.